In 1905, John Scott Haldane and Mabel FitzGerald set out to ‘ascertain the limits within which the alveolar CO2 pressure varies in different individuals’ – i.e. they set out to discover a baseline figure for the carbon dioxide (CO2) pressure in the lungs of healthy human beings – ‘as a knowledge of these limits is essential to a correct appreciation of pathological changes in the alveolar CO2 pressure’. Or to put it another way, the team needed to determine the normal range of alveolar pressure in healthy people before anybody could judge how diseases affected people’s lungs.

To obtain the data, Haldane and FitzGerald used a method and apparatus which Haldane had introduced in 1898 for measuring the percentage of carbon dioxide in the air people breathed out, widely known as the Haldane Apparatus. These measurements allowed the team to calculate the CO2 concentration or ‘pressure’ in the actual alveoli, and to draw conclusions on the exchange of CO2 and O2 between the lung and the blood – the very foundation of respiratory physiology.

Colleagues, friends and family were amongst the volunteers examined in the first set of experiments conducted at the laboratory at Haldane’s home in North Oxford, in March and April 1905. These results of these experiments were recorded by Mabel FitzGerald in one of the many notebooks which survive in her archive.

A small black notebook (pictured here with some of FitzGerald’s general notes on air analysis) – looking rather inconspicuous, but giving remarkable insights into early experiments in respiratory physiology.